The present invention relates, in general, to filtering and, more particularly, to filtering a colloidal suspension used for planarizing semiconductor wafers.
Chemical mechanical planarization (CMP) is used to planarize features in the manufacture of advanced integrated circuits. CMP is used in almost all stages of semiconductor device fabrication. For example, chemical mechanical planarization allows the creation of finer geometry structures via local planarization and for global wafer planarization to produce high density vias and interconnect layers. Materials that undergo CMP in an integrated circuit manufacturing process include single and polycrystalline silicon, oxides, nitrides, polyimides, aluminum, tungsten, and copper.
In the semiconductor industry, a semiconductor wafer is held by a wafer carrier of a chemical mechanical planarization tool during a polishing process. Thus, CMP is also referred to as chemical mechanical polishing. A slurry comprising a colloidal solution that includes both abrasives and chemicals for removing materials from the semiconductor wafer is applied to the surface of a polishing media. The polishing media is compliant and provides for the transport of the slurry. The polishing media is placed on a rotating disk known as a platen. The wafer carrier brings the semiconductor wafer in contact with and coplanar to the surface of the polishing media. A predetermined force is applied by the wafer carrier to ensure the slurry abrades the surface of the semiconductor wafer. Typically, both the wafer carrier and the platen are rotating during the polishing process.
The type of chemicals and abrasives used in the polishing process vary depending on the materials being removed from the semiconductor wafer. The limits of the polishing process are, in a large part, controlled by the size of particles in the polishing slurry. Semiconductor manufacturers typically do not filter polishing slurry during semiconductor wafer processing. Filtering is very costly if used on colloidal suspensions due to filter cost and the need for continuous maintenance of the filters. There are also problems with particle shedding from the filter, low flow rates due to blinding, and loss of adequate solids in the colloidal suspension. The absolute limit on particle size is determined by the chemical supplier producing the polishing chemistry. The time delay between shipment and usage at the semiconductor manufacture site allows the polishing slurry to agglomerate producing larger particles. Mechanisms that increase agglomeration are chilling, drying, and excessive agitation. The larger particles produce scratches on the semiconductor wafer during the polishing process that can affect wafer yields and product reliability.
Accordingly, it would be advantageous to have a filter capable of filtering a colloidal suspension with a flow rate that allows real-time filtering in an industrial application. More specifically, it is desirable that the filter allows for point-of-use filtering on a chemical mechanical planarization tool, reduces particle size to an optimal number, and increases uniformity of the polishing slurry. It would be of further advantage for the filter to require little or no maintenance and have no impact on the semiconductor wafer throughput in the factory.